Radio Frequency Heating

Radio Frequency Heating

1. Indirect electro heating

   • Electrical energy
     • Electromagnetic radiation
       • Generates heat within the product

2. Combination of:

   • Dipole heating
   • Electric resistance heating

3. Advantages

   • Uniform heating in homogeneous foods
   • High penetration depth (Pasteurize or sterilize liquid products)
   • Rapid heating ( Allow faster line speeds and shorter line lengths for semi continuous as well as continuous unit operation)
   • Ease of targeting product
   • Levelling moisture
   • Avoid overheating and dehydration of product surface
   • Turn on/off instantly
   • Thermocouple

4. Principle

   • RF portion of the electromagnetic spectrum: 1-30 MHz
   • Food materials
     • store and dissipate electric energy when subjected to an electromagnetic field
     • Poor electric insulators
   • Principle of absorption of electric energy
     • Maxwell’s equations
   • Practice
     • Relative complex permittivity ɛ*=ɛ/ɛ。
       • ɛ (dielectric constant)
         • food material’s ability to store electromagnetic energy
       • ɛ" (dielectric loss factor)
         • material’s ability to dissipate electromagnetic energy
       • measures the ability of the material to interact with the electric field of RF
       • dimensionless
       • ɛ。=8.8542x10-12 F/m (Permittivity of free space)
   • 1. RF generator creates an alternating electric field between two electrodes
     • 2. Material to be heated is placed in between the electrodes
       • 3. The alternating energy causes polarization of the molecules
         • 4. Molecules continuously reorient themselves to face opposite poles
           • 5. Generates heat
             • Energy absorption
               • Primary (2 Mechanisms)
                 • Dipolar relaxation
                 • Ionic conduction
               • Secondary Mechanism
                 • Oscillatory migration of ions in the food that generates heat
   • Water
     • Dipolar
       • Water molecules try to follow the electric field associated with electromagnetic radiation as it oscillates at very high frequencies
         • Producing heat

5. Applications in Food Industry

   • Meat & Fish Products
     • Fish meal
       • Rapid and homogenous heating, better reduction of microbes
     • Ready to eat aquatic food (eg: caviar)
       • completely inactivate L. innocuacells microorganisms , good visual quality
     • Chicken meat
       • Less time require to reach end point temperature
     • Pre-packaged heterogeneous food
       • Retain product quality better
   • Liquid Foods
     • Apple juice, orange juice and apple cider
       • Effective inactivation of E. coli K12, similar colour and flavour property with no loss of ascorbic acid
     • Soybean milk
       • Inactivation of Bacillus subtilis spores
   • Drying in agricultural produce
     • Post-bake drying of cookies, crackers and pasta
       • Even out the moisture distribution
   • Disinfection in agricultural produce
     • Peaches and nectarines
       • Control brown rot
     • Black and red pepper spice
       • Inactivate Salmonella Typhimurium and Escherichia coli O157:H7

6. Disadvantages

   • High cost
   • Product factor
   • All generators and applicators must be shielded
   • Specially designed for product
   • Lack of in-depth information area